This invention relates to a multi-port device apparatus and method for analyzing the characteristics of the multi-port device having three or more input-output terminals, and more particularly, to a multi-port device analysis apparatus and method which is capable of analyzing the multi-port device having a balanced input-output terminal or a multi-port device having different input-output impedance by using a conventional unbalanced two port type network analyzer and a conventional unbalanced multi-port test set having three or more ports.
In order to analyze the characteristics of the communication devices or communication components used in various communication systems, a network analyzer is frequently used. A network analyzer obtains the data of various test parameters, such as a transfer function, reflection characteristics or a group delay of a high frequency components (device under test) used in a communication system by observing the frequency response of the high frequency components resulted in response to a sweep frequency signal.
A network analyzer is usually comprised of two ports, one input port and one output port. The input port sends a sweep frequency signal (test signal) to the device under test and the output port receives the response output signal of the device under test. The input port and the output port of the network analyzer are usually organized such that either port can be switched to the other by a switching operation. An example of schematic structure of such a network analyzer is shown in the block diagram of FIG. 1.
The configuration and operation of the network analyzer which is shown in FIG. 1 is briefly explained. A network analyzer 10 has two input-output ports P1 and P2 which are connected to bridges (or directional couplers) 11 and 12, respectively. Each of the bridges 11 and 12 functions as a signal separation circuit. A test signal from a signal generator 15 is sent to one of either the bridge 11 or bridge 12 which is selected by a switch 13. The test signal is sent from the selected one of the port P1 or port P2 to the device under test. The test signal from the signal generator 15 is also sent to the inside of the network analyzer as a reference signal. Namely, this reference signal and the input signal from the bridge are respectively provided to frequency converters 17, 18 and 19 whereby converted to signals of lower frequencies. The frequency converted input signal and the reference signal are respectively converted to digital signals by corresponding AD converter 21, 22 and 23. These digital signals are processed by a digital signal processor (DSP) 25 to obtain those data such as transfer functions, scattering parameters, and group delays. The data showing these characteristics are displayed by a display 29 in various formats under the control of a CPU 28 which controls the overall operation of the system.
The devices to be tested, which are components such as used in the communication systems, are sometimes formed with not only two terminals but also three or four terminals (hereinafter may be referred to as xe2x80x9cmulti-port devicexe2x80x9d if necessary). In order to analyze the characteristic of the multi-port devices by using the network analyzer comprising two ports, the measurement can be performed by terminating either one of the terminals of the device 30 to be tested by the characteristic impedance as shown in FIG. 2A. However, since this configuration causes various problems, the configuration using a multi-port test set as shown FIG. 2B is employed. The multi-port test set is provided between the two port network analyzer and the multi-port device to perform the characteristic analysis of the multi-port device accurately as well as easily. The connections of the components among the multi-port test set 20, the network analyzer 10 and the multi-port device 30 are shown in FIG. 2B. In this example, the multi-port test set 20 includes four input-output ports Q1-Q4.
In the network analyzer or the multi-port test set in a high frequency band as described above, each of the ports is in an unbalanced form and the input-output impedance is fixed to 50 ohm (or 75 ohm). Also, in the past, most of the conventional devices to be tested are configured in the unbalanced form with the impedance of 50 ohm. However, owing to the recent development of the semiconductor technology as well as the advancement and complication in the communication system, some of the recent multi-port devices to be tested employ the configurations which are different from that of conventional devices to be tested. An example of a basic structure of such a multi-port device 40 is shown in the circuit diagram of FIG. 3. In this example, an input terminal T1 is an unbalanced type and its impedance is 50 ohm while between output terminals T2 and T3 is formed of a balanced type with an impedance of 150 ohm.
Under the conventional technology, the testing of the balanced type multi-port device having a relatively high impedance as described above by using an unbalanced type network analyzer or a multi-port test set having a low impedance is performed according to the configuration as shown in FIG. 4. Namely, a balance-unbalance converter 42 is connected to the device 40 to be tested thereby converting a balanced output of the device to be tested to an unbalanced output. The input terminals T4 and T5 of the converter 42 are a balanced type and have 150 ohm impedance therebetween, and are connected to the output terminals T2 and T3 of the device 40 to be tested, respectively. The output terminal T6 of the converter 42 is formed as an unbalanced type and has an impedance of 50 ohm. Accordingly, the characteristic of the device to be tested is obtained by connecting the input terminal T1 and the output terminal T6 to the network analyzer.
According to the conventional measuring method using this converter, the measured value of the device under test 40 alone cannot be obtained because the measured result includes the characteristics of the balance-unbalance converter 42. In addition, owing to the use of the converter 42, even though the characteristic of the input terminal T1 and the output terminal T6 and the characteristic between these two terminals can be measured, the characteristic of other terminals cannot be obtained. For example, the characteristic of the balanced output terminals of the device under test cannot be obtained. In addition, because the balance-unbalance converter 42 needs to have the function to convert the output impedance of the device to be tested into the impedance of the multi-port test set 20 or the Network analyzer 10, it is necessary to prepare various kinds of converters in accordance with the impedance value of the devices to be tested.
Therefore, it is an object of the present invention to provide a multi-port device analysis apparatus and method which is capable of accurately measuring a multi-port device under test having an input-output terminal structure or an impedance different from that of the conventional devices to be tested.
It is another object of the present invention is to provide a multi-port device analysis apparatus and method which is capable of measuring a multi-port device having a balanced output ports without using a balance-unbalance converter.
It is a further object of the present invention is to provide a multi-port device analysis apparatus and method which is capable of measuring a multi-port device having a balanced port by using a multi-port test set or network analyzer having unbalanced input-output ports.
It is a further object of the present invention is to provide a multi-port device analysis apparatus and method which is capable of measuring a multi-port device having a impedance different from the impedances of the multi-port test set or net work analyzer by using such a multi-port test set and a network analyzer.
In order to test the multi-port device having three or more ports, the multi-port device analysis apparatus of the present invention is comprised of:
a network analyzer organized such that one port produces a test signal while the other port receives an input signal to analyze the characteristic of a device under test in vector values;
a multi-port test set connected to the ports of the network analyzer for converting the ports of the network analyzer to three or more of the ports by a switch provided therein;
wherein the multi-port device under test is connected to the multi-port test set without using a balance-unbalance converter thereby analyzing the characteristic data of the device in vector values.
Further, the multi-port device analysis apparatus of the present invention performs a calibration process of the analysis apparatus including cables connecting the multi-port device to be tested in a state where the network analyzer and the multi-port test set are connected with each other, stores the error correction data thus obtained in the network analyzer, and connects the multi-port device to be tested to the multi-port test set without using a balance-unbalance converter to obtain the characteristic vector data of the device, and analyzes the device by performing the error correction of the characteristic vector data by applying the error correction data.
Further, the multi-port device analysis apparatus of the present invention analyzes the multi-port device under test by obtaining the characteristic vector data at each terminal of the multi-port device under test and converting the vector data at each terminal into the data corresponding to the optional impedance value. Also, the multi-port device analysis apparatus analyzes the characteristic of the device under test by obtaining the characteristic vector data at each unbalanced terminal and converting such vector data at each unbalanced terminal into balanced terminal data between two optional terminals.